High-frequency apparatus



' Jan. 2, 1945. P E Efi 2,366,556

HIGH FREQUENCY APPARATUS Original Fild March 1, 1940 2 Sheets-Shget 1 z z Z T0 BATTERY BATTERY Mb 7 OUTPUT Irfiventor; John P. Blewett,

His Attorneg.

Jan. 2, 1945- J. P. BLEWETT HIGH FREQUENCY APPARATUS Original Filed March 1, 1940 2 sheets sheet 2 Inventor: Jo n P. Blewett,

His Attorney.

Pa tente d Jan. 2, 1945' I aacassc BIGHFEREQUEN CY llohn P.'Blewett, Scotti, N.Y'.;-assignortiiflenora l 'Electric fiompany wcorporafleuotNowioit h origami .alullication .March ion, No.

.Dividedand 37, 194 1, Serial 'No."3 85,437

The invention described herein was previously described in application ,Serial No. 321,746,;nled March 1, 1940, as a Joint applicationof Simon Rama and JohnP; Blewett. i

I The invention relates to other conversion effects at frequencies so high that electron transit time considerations play a controlling part in the operation. of .theapparatus.

In certain respects the invention representsan application of the so-called velocity modulation principles,. which are described in- U. S, Patent 2,220,839, granted November 5,1940, in the :name. of W. C. Hahn. However, whereas Hahnhas employed an elongatedtbeam tuhe of the-cathode my type for prqducingthe. effects desired, the present invention utilizes .a structurein which the electron beam is caused to traverse a more or less helical. path,.thus realizing agreater degree of compactness as well as various operational advantages which will be explaine in the following.

The generic aspects of helical-path devicesof. I the type in question are claimedin the aforesaid prior application Serial N 0. 321,746, and the present case. relates specifically to a particular :and especially advantageous arrangement by which the invention disclosed in the .priorapplication may be carried out. -Briefl stateithis arrange; ment comprises thelcombination of an 61 mg at ed I linear cathode, means for producing orbital motioncf electrons emitted by the cathode and for causing the orbitally moving electrons to DIG, gress axially along the cathode, and means acting on the axially progressing electron stream at mutually spaced regions to produce useful high frequency efiects.

.The invention maybestbe understood byreference to the following description takenin connection with the drawings, in which Fig. 1 represents a diagrammatic perspective view of, an apparatus suitably embodying-the invention; Figs. 2 and 3 are partialse'ctional views respectively takenon lines 22 and 34. of Fig. l, and Figs. 4 to 6 are diagrammaticrepresentationsuseful in explaining the invention.

Referring particularly to Fig. 1 there is shown an evacuated envelope I which encloses anelongated linear cathode, consisting, for example, of an activated metal filament. In the arrangement shown, the emissive portion or the cathode is limited to the region between the points'e and 1,. although this is byfno means an essential condition. Surrounding the. cathoderan extending improvementsin elec-g, tronic apparatus for obtainingamplification and generally. eoaxia ymthit there is provided a high frequ cy. electrode. system. including a series or mutuall gseparatedcylindrical parts [2. to It. thefunction. of is described in detail in thel'nllowing. e 7 .The .cylmderi-i2,.iwh i, ch subtends a gnaiior portionof .thedathode 1 i, ismaintaind at positive potential with respectto therfcathode. so as to produce lradial motion of. the electrons emitted from it. "This motion is converted into orbital motion by. means of.a.strong,magnetic field established .ln'aidireetion parallel to the cathode, forexample, .by.means.ot a coil 19. rectional potential is impressed between the electrndeiiZ and the. electrode 113 for producing an axialfleldadante'd to causethe electrons to move axially along theelectrode-system in the directionof thebiaber-numhered electrodes. If dered further potentials may be applied totheotherelectrodes' of thesystem (i. e'. theelectrode ll, I5 and i B.) to increase this axial motion, .but satisfactory-Dperation of the apparatus will .be obtained if. all these parts are at a common potential .witnthe electrode. A direct currentsource suchas'a battery '20 may be employed tomaintainthepotential relationships. referredto.

.As appearsmoreiclearlyin.Fig. 2, the electrode zlicons'istslof a split cylinder havingtwo 3O semi-cylindrical conducting parts 13a and 132), which are .insulatingly spaced and which define a generally vcylindrical chamber. between them. In the use or the annaratusthese-parts are ub- J'ected'to an alternating difference of potential by meansonan appropriate input circuit which is illustrate diagrammatically a including a pair of,.paralle1econductors ii and 22. These conductors are ..as sumed. to constitute .a standing wave transmission line -,(e,g.a quarter wave line) ahigh frequency signal source. A;common battery' connection-23 for the' two conductors is .pro-

vided for maintainingthe average. potential ofthe electrodeparts l3a.and.|-3b.at adesired value.

Before explaining theroperationofthe apparatus .as soutar-gdescribed it will .be helpful to refer to thelmattersrepresentedin Figs. .4.to 6.

In Fig. 4, B. may.- betaken .to represent .theapath, or an-electron lwhose velocity corresponds to average. or .nnmbdulated velocity of :an.-eleetr0n-..stream of. "which it forms a .part.

The point --0 is considered torepresent a region in which the stream is subjected .to a high irequency. modulating potential. electron which paesev-.fl el ma nsfaeenwd is h Ph which maybe. eikcited'in any desired. fashion from V smaller orbit as indicated potential gradients.

decelerated electrons seek being indicated at b and b'..

as to be accelerated thei eby may bev expected to follow a path of somewhat greater radius than the path B, such enlarged path being represented, for example, by the dot-dash line C. n the other hand. decelerated electrons will describe a by thedotted' linel). Theoretical analysis shows, however, that each electron will require precisely traverse its orbit and return to the Moreover, it is found point 0.

coincident with that of its initial transit.

Fig. 5 shows the wayin which the considerations discussed above are affected by the presence of a component of axial velocity in the electron stream motion. Thus, in this figure, the solid line E represents the projected'path of a hellcally moving electron of average velocity, while the dotted lines F and G respectively show (in side projection) the lines followed by electrons which are respectively accelerated and decelerated' by the effect of modulating potentials applied as the va ious electrons traverse the region occupied by the line-0. It will be noted that for that each electron will pass through the point 0 along a line. substantially of the beam characterized by a high degree of "charge density modulation, that is, cyclical variation of elec-'- the same time to therefore besaid that at j density modulation of the beam is negligible.

Y the region 0",

tron density with time.

.a region displaced ninety considered, that is to say,

0 and'c', substantially no variations of the charge degrees from that iust observed, and it'may this point the charge density withrtime will be The condition of negligible charge density I modulation last referred to will be realized again when the beam retdrns -to its starting'point at be characterized by its initial, relatively uniform charge density, although the velocity variations produced by the primary modulating action of the modulating system will still exist in the viously explained. Therefore, since the charge,

while for the case I beam. Upon a further traversal of the gap by the electron stream, these variations will be increased in accordance with the principles predensity modulation occurring between planes 1) and b is afunction of thejvelocity variation which produces it, it is apparent that such charge density modulation will be greater for each successive orbital passage of the electron stream.

If desired, this effect-may be still further inthe action of acircularly movdiagrammatically in Fig. 6, which 'may be taken I to show the conditions occurring at various points around the orbit of an electron stream which is caused to traverse a modulating gap For the case illustrated; it is assumed of potential variation across at 0". that thefrequency the gap is such that eight variation occur during the time required for a single electron to traverse its orbit. The solid dots a may be taken to represent individual electrons, and considered in the aggregate, they show the condition of the beam at a particular instantoftime.

As the various electrons move azimuthally, those whose velocity exceeds the average beam velocity seek an orbit of greater radius, while the radius. As a consequence of this action, observations taken between various closely spaced azimuthal planes will show density measured at most points around the electron path varies material1y with time. This variation is mainly a function of the relative displacement of the centersof gyration of the various electrons and 'is found to be greatest between planes which are locatedapproximately ninety mechanical degrees from 0", such planes It will be noted that at the instant which is represented in Fig. 6, considerable bunching of the electrons exists betweenthe planes referred to at the upper side a relative paucity of electrons is to be noted hean orbit of reducedthat the electroncomplete cycles of for April 1,

. the structure. 'It may be observed in the first and repetitively traverse the said interelectrode.

of the electron orbit, while tween the same planes at the other si'd'eof the orbit. On the other hand,'this situation would creased by providing additional modulating means arranged to operate in the beam as it passes the region c-c'. Such modulating means should, of'course, be correlated to the means acting at the point'n in order to assure that the.

reiilts obtained 'shall be of cumulative charac r.

As a result of the considerations stated -in the foregoing, even a relatively slight velocity modulation produced at the modulating gap ii" may, by additive action, be made to cause relatively great charge density variations in the region b-b'. Therefore, if some means are provided by which-the charge density variations existing at b-b' can be utilized in an appropriate manner, the system as a whole may be employed for amplification purposes.

While the foregoing does not represent a com-' plete statement of the theory applicable to the structure of Fig. 1 (a more-exact treatment'is given in an article by John P. Blewett'and Simon Ramo at pages'635-64l of the Physical Review 1940) it provides anapproximate viewpoint ,useful in visualizing theoperation of place that the input circuit 2l-22 functions to produce cyclically variable voltages across the I gaps which separate the electrode parts I31: and i3b.- In accordance with the discussion given above, therefore, it may be assumed that if the circumferential dimensions of the parts are properly correlated to theorbital velocity of the electrons and to the operating frequency of the syste cumulative modulation effects may be obtained as the various electrons successively gaps. Moreover, the velocity variations thus prof duced may be expected to. result in even greater charge density variations in the more advanced.

portions of the electron stream.

Useful output voltages are obtained with the.

apparatusdescribed above trode i5 also of a split cylinder construction, as

- shown finFig. 3 andby connecting the parts l5a be found to be reversed at an instant taken a It is, therefore, apparent that the electron orbit the portion half-cycle later. on-either side of and Hi) to an appropriate output circuit which is represented diagrammatically as including apair of parallel conductors 24 and 25. As the between the planes 1 and b will be On the other hand, in

between the planes and at this point'the beam wlll' by making the elecvariationsexistingin the electron stream at a various components of thepreviously modulated beam successively traverse the gaps existing between the electrode parts I54: and 15b, excitation of these parts will be produced, andan output voltage of significant magnitude (i. e. greater than the magnitude of the input voltage) will be developed across the terminals of the output circuit. After its passage through the electrode- IS the electron stream may be collected by means of an appropriately positioned anode 26.

It is desirable with the construction above described to prevent radially moving electrons from reaching the surface of the envelope l and thus producing objectionable wall-charging. To this end'the electrodes l2, l4 and 16 are provided with flanged extensions 21 which overlap the interelectrode gaps and prevent egress of electrons. Functionally similar flanges 28 are provided in connection with the longitudinally extending gaps which exist between the respective parts of the electrodes |3 and I5.

It will be noted that in the construction of Fig.

region which is displaced from the said first region in a direction along the axis of progression 1, the input and output gaps are in a common plane rather than being 90 degrees displaced as might be expected from the discussion given in connection with Figs. 4 and 5. The possibility of this arrangement, which has been found satisfactory for a particular condition of operation, is explained in part by the relatively. great efiect of space charge in a system in which the electron source comprises a central filament as above described. In this situation, the theoretical considerations which indicate a quadrangular displacement of the input and output gaps for cases of relatively low electron density no longer apply with complete accuracy, but a determination of the best relationship between the location of the input gaps and the location of the output gaps may readily be made by experimental methods.

-It should also'be pointed out in connection with the apparatus of Fig. 1 that the arrangement shown does not necessarily permit all the emitted electrons to follow orbits of uniform radius. It appears, howeventhat the net effect is to establish a rotating and axially progressing space charge which producw high frequency effects generally indistinguishable from those caused by an electron stream whose form and course are more definitely fixed.

In th foregoing the invention has been described by reference to particular embodiments.

It will be understood, however, that numerous modifications may be made by those skilled in a the art without departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure. What I claim as new and desire to secure by Letters Patent of the United States is: I

1.-In high frequency apparatus, the combination which includes a generally linear cathode, means for producing radial motion of electrons emitted from said cathode and for converting such radial motion into orbital motion about the cathode, means positioned at a first region along the axis of the cathode for producing cyclically 'variable potential gradients which act at least partially tangentially to the orbital path of the electrons thereby to develop variations in the orbital velocities of the erectrons as they traverse such region, means for producing axial progression of theorbitally moving electrons along the cathode, and energy-abstracting means including .an output circuit arranged to be affected by the of the stream. 7

2. In high frequency apparatus, the combination which includes a generally linear cathode, means for producing radial motion of electrons emitted from said cathode and for converting such radial motion into orbital motion about the oathode, spaced conducting parts defining a relatively elongated gap which xtends parallel to the oathode in proximity to the outer boundary of the orbitally moving electron stream, means for applying a high frequency voltage between the said conductive parts to vary the orbital velocity of the electrons in accordance with the variations of the potential gradients thus established across the said gap, means for producing axial progression of the orbitally moving electrons along the cathode, another pair of spaced conducting parts defining a second gap which extends generally parallel to the first gap and in a region which is displaced therefrom in a direction along the axis ,of progression of the stream and circuit means connected between the second named pair of conance with the variations which exist in the electron stream upon its traversal of the said second p- I 3. In high frequency apparatus, thecombination which includes an elongated cathode, an electrode system including at least two aligned tubular electrode structures coaxial with the cathode, said two structures being each axially divided into two mutually spaced parts having gaps between them, a field-producing system for causing radial motion of electrons emitted from the cathode and for converting said radial motion into axially progressive orbital motion along a path having the cathode as its central axis, an input circuit for applying a, high frequency voltage between the parts of one of the said divided struck tures, thereby to-develop variations in the orbital velocities of the electrons as they traverse the gaps between such parts, and an output circuit connected between the parts of th other substructures coaxially surrounding the cathode, at

least twoof the structures being divided into spaced semicylindrioal parts defining axially extending gaps between their opposed edges, means for applying an electric field between the oathode and at least certain ones of the said structures to produce radial motion of electrons emitted by the cathode, means producing a magnetic field extending axially of the cathode to convert the radial motion of the emitted electrons into orbital motion, means for producing a field adapted to cause axial progression of the orbitally moving electrons, means for applying a high frequency voltage between the semicylindrical parts comprising one of the said divided structures,

thereby to develop variations in the orbital veloc-.

ities of the electrons as they traverse the gaps between such parts, and an output circuit connected between the parts of the other divided structure and responsive to variations existing i the. electron stream as it traverses such parts.

JOHN P. BLEWETI. 

